Semiconductor device and method of forming the same

ABSTRACT

A semiconductor device includes a board and a semiconductor chip which is connected to an upper surface of the board via face-down bonding. The semiconductor device further includes a frame-shape member which is connected to the upper surface of the board with first adhesive, and has an opening to accommodate the semiconductor chip therein, and a plate-shape member which is situated to cover the semiconductor chip and the frame-shape member, and is connected to the semiconductor chip and the frame-shape member with second adhesive, wherein the frame-shape member has such a sufficient sturdiness as to prevent thermal-expansion-induced deformations of the board and the plate-shape member.

This application is a continuation-in-part of prior application Ser. No. 08/924,958 filed Sep. 8, 1997 which is a division of Ser. No. 08/782,381 filed Jan. 13, 1997 (Pat. No. 5,729,435, issued Mar. 17, 1998) which is a continuation of Ser. No. 08/423,632 filed Apr. 17, 1995 (abandoned).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to semiconductor devices, and more particularly relates to a semiconductor device of the ball grid array (hereinafter referred to as BGA) type and a method of forming the same.

In recent years, there has been a significant increase in circuit density of semiconductor devices, and, also, there has been an increasing demand for a higher density in implementing semiconductor devices. This leads to more attention being paid on semiconductor devices of the BGA type, which can make intervals of nodes wider than can those of the QFP type, and, also, can be implemented more closely to each other.

There has been also an increase in frequencies of signals processed by the semiconductor devices. Thus, semiconductor devices of the BGA type desirably have configurations which are suitable for the processing of high frequency signals

Also, the amount of heat generated by semiconductor chips has a tendency to increase as the semiconductor chips are made in higher circuit densities. Thus, semiconductor devices of the BGA type are required to have structures which are suitable for releasing heat.

2. Description of the Related Art.

FIG. 1 shows a semiconductor device of the BGA type disclosed in the U.S. Pat. No. 5,166,772.

A semiconductor device 10 includes an assembly board 11, a semiconductor chip 12 fixed to a central portion of an upper surface of the assembly board 11, solder balls 13 arranged at nodes of a grid pattern on a lower surface of the assembly board 11, and a cover 14 made of a resin for sealing the semiconductor chip 12.

In FIG. 1, wires 17 couple between pads 15 on the semiconductor chip 12 and pads 16 on the assembly board 11.

FIG. 2 shows an enlarged plan view of the assembly board 11 of FIG. 1. FIG. 3 shows a cross-sectional view of the assembly board 11 taken along a line shown as A—A in FIG. 2. As shown in FIG. 3, the assembly board 11 includes a printed board 20 and an additive layer 21 provided on the printed board 20. The assembly board 11 also includes through-holes 22 ₁ to 22 ₅.

Each of the pads 15 on the semiconductor chip 12 is electrically connected to a corresponding one of the solder balls 13 provided beneath the assembly board 11. For example, as can be seen in FIG. 1, FIG. 2, and FIG. 3, a pad 15 ₁ is connected to a solder ball 13 ₁ via a wire 17 ₁, a pad 16 ₁, a wiring pattern 23 on the additive layer 21, and a through-hole inner layer 24 provided on an inner surface of the through-hole 22 ₂.

In this configuration, the through-holes 22 ₁ to 22 ₅ are open holes, so that the additive layer 21 cannot be formed at the locations of the through-holes 22 ¹ to 22 ₅. Thus, wiring patterns on the additive layer 21 cannot be formed in such manner that they traverse the locations of the through-holes 22 ₁ to 22 ₅.

This leads to a restriction on formation of wiring patterns such that paths of the wiring patterns cannot be laid freely.

Take an example of forming a wiring pattern connecting the pad 15 ₁ and the through-hole 22 ₂. A straight wiring pattern 25 as shown by dotted lines in FIG. 2 cannot be formed. Thus, the wiring pattern 23 ends up having a bending shape detouring from a straight line in order to avoid the through-holes 22 ₁ and 22 ₅.

As a result, the wiring pattern 23 is bound to have a longer path length than otherwise. This is undesirable in terms of signal propagation, since signals having high frequencies may be distorted in the longer path.

Since the semiconductor chip 12 is sealed by the cover 14, it is difficult for heat generated by the semiconductor chip 12 to be transferred to the outside. Namely, the semiconductor device 10 is not suitably structured in terms of releasing heat.

Accordingly, there is a need in the field of semiconductor devices for a semiconductor device in which there is no restriction on formation of wiring paths and heat can be released with ease, and for a method of forming that semiconductor device.

Also, there is a need for a semiconductor device in which there is a wider scope for an arrangement of wirings for external connection.

SUMMARY OF THE INVENTION

Accordingly, it is a general object of the present invention to provide a semiconductor device and method of forming the same which satisfies the need described above.

It is another and more specific object of the present invention to provide a semiconductor device in which there is no restriction on formation of wiring paths and heat can be released with ease.

In order to achieve the above objects, a semiconductor device according to the present invention includes a board base having through-holes filled with a filling core, an additive layer provided on an upper surface of the board base as well as an upper surface of the filling core, wherein the additive layer includes a wiring pattern having one or more paths, a semiconductor chip fixed on an upper surface of the additive layer, and nodes provided on a lower surface of the board base, wherein one or more paths are laid out without a restriction posed by the through-holes, and are used for electrically connecting the semiconductor chip and the nodes.

Thus, according to the present invention, the through-holes are filled with the filling core, so that a single flat surface can be obtained, which is flush with the upper surface of the board base. This leads to the additive layer being formed on portions of the through-holes. With the additive layer covering the entire surface, there is no need to get around the through-holes when laying a wiring pattern.

Also, in the semiconductor device described above, the semiconductor chip can be fixed with its face down on the upper surface of the additive layer by a bonding process. Then, the semiconductor device can include a dam member having a frame shape and adhered to the upper surface of the board so as to surround the semiconductor chip, and a metal plate adhered to a back surface of the semiconductor chip and to the dam member.

Thus, according to the present invention, the metal plate adhered to the back surface of the semiconductor chip can release the heat generated by the semiconductor chip.

It is yet another object of the present invention to provide a method of forming a semiconductor device in which there is no restriction on formation of wiring paths.

In order to achieve the above object, a method of forming a semiconductor device according to the present invention includes the steps of forming through-holes through a board base, forming through-hole inner layers inside the through-holes by plating metal and by etching the metal to leave the through-hole inner layers, filling the through-holes with a synthetic resin, forming an insulator layer on the board base and on the synthetic resin filling the through-holes, forming a wiring pattern on the insulator layer by plating conductive metal and by etching the conductive metal to leave the wiring pattern, fixing a semiconductor chip over the board base, and forming nodes beneath a lower surface of the board base.

Thus, in the semiconductor device formed by the method described above, the through-holes are filled with the synthetic resin, so that there is no need to get around the through-holes when laying the wiring pattern.

It is still another object of the present invention to provide a semiconductor device in which there is a wider scope for an arrangement of wirings for external connection.

In order to achieve the above object, a semiconductor device according to the present invention includes a semiconductor chip having first electrodes on one surface thereof and at least one second electrode on another surface thereof, a board having first wirings and second wirings for external connection, wherein the first wirings are connected to the first electrodes so that the semiconductor chip is mounted on the board, and a conductive member covering the semiconductor chip so as to electrically connect at least one second electrode with the second wirings.

Thus, in the semiconductor device described above, at least one second electrode can be electrically connected with the second wirings via the conductive member. Since the conductive member completely covers the semiconductor chip, the second wirings can be anywhere around the semiconductor chip to be electrically connected to the conductive member. Thus, there is a wider scope for the arrangement of the second wirings for the external connection.

Other objects and further features of the present invention will be apparent from the following detailed description when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partially sectional isometric view of a BGA type semiconductor device of the related art;

FIG. 2 is an enlarged partial plan view of an assembly board of FIG. 1;

FIG. 3 is a cross-sectional view of the assembly board taken along a line A—A in FIG. 2;

FIG. 4 is a partially sectional isometric view of a first embodiment of a BGA type semiconductor device according to the present invention;

FIG. 5 is a cross-sectional view of the BGA type semiconductor device taken along a line II—II in FIG. 4;

FIG. 6 is an enlarged partial plan view of an assembly board of FIG. 4;

FIG. 7 is a cross-sectional view of the assembly board taken along a line IV—IV in FIG. 6;

FIGS. 8A to 8E are process charts explaining a process of forming the assembly board of FIG. 4.

FIG. 9 is a partially sectional isometric view of a second embodiment of a BGA type semiconductor device according to the present invention;

FIG. 10 is a partially sectional isometric view of a third embodiment of a BGA type semiconductor device according to the present invention;

FIG. 11 is a partially sectional isometric view of a fourth embodiment of a BGA type semiconductor device according to the present invention;

FIG. 12 is a partially sectional isometric view of a fifth embodiment of a BGA type semiconductor device according to the present invention;

FIG. 13 is a partially sectional isometric view of a sixth embodiment of a BGA type semiconductor device according to the present invention;

FIG. 14 is a partially sectional isometric view of a seventh embodiment of a BGA type semiconductor device according to the present invention;

FIG. 15 is a partially sectional isometric view of an eighth embodiment of a BGA type semiconductor device according to the present invention;

FIG. 16 is a partially sectional isometric view of a ninth embodiment of a BGA type semiconductor device according to the present invention;

FIG. 17 is a cross-sectional view of a tenth embodiment of a semiconductor device according to the present invention;

FIG. 18 is an enlarged partial view of the semiconductor device of FIG. 17;

FIG. 19 is an enlarged partial view of the semiconductor device of FIG. 17;

FIG. 20 is an enlarged partial view of the semiconductor device of FIG. 17;

FIG. 21 is a cross-sectional view of an eleventh embodiment of a semiconductor device according to the present invention;

FIG. 22 is a cross-sectional view of a twelfth embodiment of a semiconductor device according to the present invention;

FIG. 23 is a cross-sectional view of a thirteenth embodiment of a semiconductor device according to the present invention;

FIGS. 24 and 25 are illustrative drawings for explaining a fourteenth embodiment through a sixteenth embodiment of the present invention; and

FIG. 26 is a table chart showing results of experiments which were conducted to check the number of defective devices after performing a temperature-cycle test on semiconductor devices.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following, embodiments of the present invention will be described with reference to the accompanying drawings.

FIG. 4 and FIG. 5 show a partially exposed isometric view and a cross-sectional view, respectively, of a first embodiment of a BGA type semiconductor device 30 according to the present invention.

The BGA type semiconductor device 30 includes an assembly board 31, a semiconductor chip 32, a dam member 33, a metal plate 34, and solder balls 13A.

The semiconductor chip 32 has solder bumps 40 on a surface 32 a thereof. The semiconductor chip 32 is fixed with its face down to a central portion of the assembly board 31 by a flip-chip method soldering the solder bumps 40 with pads 41 on the assembly board 31.

The dam member 33 is formed from the same material as that of the assembly board 31, and has a shape of a rectangular frame. The dam member 33 is adhered to a perimeter area of the assembly board 31.

The metal plate 34 is adhered to the dam member 33 at a peripheral area of a lower surface thereof so as to cover the semiconductor chip 32. Thus, a space 42 of the semiconductor device 30 containing the semiconductor chip 32 is sealed.

A paste layer 43 is provided between a back (upper) surface 32 b of the semiconductor chip 32 and the metal plate. The paste layer 43 is formed from an insulating paste having a high heat transfer characteristic which is supplemented by fillers such as AlN, diamond, and the like.

Another paste layer 44 is provided between the semiconductor chip 32 and the assembly board 31. The paste layer 44 is formed from an insulating paste having a high heat transfer characteristic.

Each of the solder bumps 40 of the semiconductor chip 32 is electrically connected with a corresponding one of the solder balls 13A.

FIG. 6 and FIG. 7 are an enlarged plan view and a cross-sectional view, respectively, of the assembly board 31.

As shown in FIG. 7, the assembly board 31 includes a printed board 50 as a board base and an additive layer 51 provided on the printed board 50. The additive layer 51 includes a wiring pattern 23A. Through-holes 22A₁ to 22A₅ are formed only through the printed board 50, and have through-hole inner layer 24A₁ to 24A₅ made of Cu. Also, each of the through-holes 22A₁ to 22A₅ is filled with a filling core 52 formed from a synthetic resin.

Thus, the additive layer 51 is formed on the printed board 50 at an area other than the through-holes 22A₁ to 22A₅, and is formed on a upper surface 52 a of the filling core 52 at the through-holes 22A₁ to 22A₅. Portions of the additive layer 51 which are directly above the through-holes 22A₁ to 22A₅ are shown as through-hole portions 53 ₁ to 53 ₅.

Since the additive layer 51 does not have an opening, paths of wiring patterns can be laid on any place of the additive layer 51. In other words, there is a wider scope for the formation of wiring patterns without a restriction posed by through-holes 22A₁ to 22A₅, as compared to the related art.

As shown in FIG. 6, a wiring pattern 23A is formed to traverse the through-hole portions 53 ₄, 53 ₅, and 53 ₂. One end of the wiring pattern 23A is coupled to the through-hole inner layer 24A₂ via a via 54.

In the related art, a wiring pattern 23B would have to get around the through-holes as shown by dotted lines in FIG. 6. In contrast, the wiring pattern 23A in the case of the present invention is straight, and, thus, has a path of the shortest length.

In FIG. 4, the solder bump 40 ₁ of the semiconductor chip 32 is electrically connected to the solder ball 13A₁ beneath the assembly board 31 via the pad 41 ¹, the wiring pattern 23A, the via 54, and the through-hole inner layer 24A₂. The semiconductor device 30 is implemented on a printed board (not shown) via the solder bumps 13A.

Characteristics of the semiconductor device 30 in operation will be described below.

[Characteristics for High Frequency Signals]

The wiring pattern 23A is laid on the shortest path, and there is no wire used in the flip-chip method. Thus, signals having a high frequency can be conducted well without a distortion. Thus, the semiconductor device 30 has a desirable characteristic regarding high frequency signals.

[Characteristics for Heat Release]

With reference to FIG. 5, heat generated by the semiconductor chip 32 is conducted to the metal plate 34 via the paste layer 43, which path is shown by an arrow 60. Then, this heat is extended within the metal plate 34 as shown by arrows 61, and is released into the air as shown by arrows 62.

Also, heat generated by the semiconductor chip 32 is transferred to the assembly board 31 via the paste layer 44, which path is shown by an arrow 70. Then, this heat is released into air as shown by arrows 72 after extending within the assembly board 31 as shown by arrows 71.

Accordingly, heat resistance within the semiconductor device 30 is smaller than that of the semiconductor device 10 of FIG. 1, so that heat produced by the semiconductor chip 32 can be released more effectively than in the related art.

A method of forming the assembly board 31 will be described below with reference to FIGS. 8A to 8E.

As shown in FIG. 8A, a through-hole forming process 80 is carried out to create the through-hole. Then, a through-hole inner layer forming process 81 is carried out, as shown in FIG. 8B, to form the through-hole inner layer 24A₂, 24A₄, and 24A₅ by plating Cu and etching the Cu plate.

Then, a through-hole filling process 82 is carried out to fill a synthetic resin in the through-holes 22A₂, 22A₄, and 22A₅, as shown in FIG. 8C. All the through-holes 22A₂, 22A₄, and 22A₅ are filled to create the filling core 52.

Then, an insulator layer forming process 83 is performed in order to form the additive layer 51. As shown in FIG. 8D, an insulator layer 56 is formed completely over the printed board 50 including portions of the through-holes. Also, the via-hole 57 is formed through the insulator layer 56 at a predetermined location.

Then, a wiring pattern forming process 84 is performed. This is done by plating Cu and etching the Cu plate so as to form the via 54 and the wiring pattern 23A as shown in FIG. 8E. Finally, gold (Au) is plated on the surface.

In the following, other embodiments of the present invention will be described with reference to FIG. 9 and the following drawings. In the figures, the same elements as those of FIG. 4 through FIGS. 8A to 8E are referred to by the same numerals, and will not be given a further description.

FIG. 9 shows a second embodiment of a BGA type semiconductor device 90 according to the present invention.

A metal plate 34A has a rectangular opening 91 at the center thereof. The rectangular opening 91 is smaller than the semiconductor chip 32. A portion of the lower surface of the metal plate 34A around the opening 91 is adhered to the semiconductor chip 32 at an edge proximity thereof. Thus, a space 42 is sealed.

A back surface 32 b of the semiconductor chip 32 is exposed to air, so that heat generated by the semiconductor chip 32 can be released into air as shown by an arrow 92. Thus, an inside heat resistance of the semiconductor chip 90 is smaller than that of the semiconductor chip 30 of FIG. 4.

FIG. 10 shows a third embodiment of a BGA type semiconductor device 100 according to the present invention.

The semiconductor device 100 differs from the semiconductor device 90 of the second embodiment only in an additional heat releasing fin 101.

The heat releasing fin 101 has a portion fitted into the opening 91, and is adhered to the back surface 32 b of the semiconductor chip 32 with a paste layer 102 having a high heat transfer rate.

Accordingly, heat generated by the semiconductor chip 32 is transferred to the heat releasing fin 101 as shown by an arrow 105, and, then, is released into air as shown by an arrow 106. Thus, an inside heat resistance of the semiconductor device 100 is smaller than that of the semiconductor device 30.

FIG. 11 shows a fourth embodiment of a BGA type semiconductor device 110 according to the present invention.

The semiconductor device 110 uses a metal cap 111 instead of the dam member 33 and the metal plate 34 of FIG. 4. The metal cap 111 is adhered to the back surface 32 b of the semiconductor chip 32 and to the perimeter area of the upper surface of the assembly board 31.

The semiconductor device 110 can be constructed with a fewer number of components, compared to the semiconductor device 30 of FIG. 4. Yet, the semiconductor device 110 has an inside heat resistance as small as that of the semiconductor device 30.

FIG. 12 shows a fifth embodiment of a BGA type semiconductor device 120 according to the present invention.

In the semiconductor device 120, the cap 111A has a rectangular opening 121, which has a smaller size than the semiconductor chip 32. The back surface 32 b of the semiconductor chip 32 is exposed to air in order to better release heat.

FIG. 13 shows a sixth embodiment of a BGA type semiconductor device 130 according to the present invention.

The semiconductor device 130 has a heat releasing fin 101. The remainder of the device is the same as the semiconductor device 120 of the fifth embodiment. The heat releasing fin 101 is partly fitted into the opening 91 so as to be adhered to the back surface 32 b of the semiconductor chip 32. The adhesion is provided by a paste layer 102 having a high heat transfer rate.

FIG. 14 shows a seventh embodiment of a BGA type semiconductor device 140 according to the present invention.

In the semiconductor device 140, the semiconductor chip 32A is provided by a face-up bonding technique. There are wires 140 coupling the semiconductor chip 32A with the assembly board 31. A resin package 141 covers the semiconductor chip 32A and the wires 140 to seal those elements. The resin package 141 is formed by putting the resin inside the dam member 33.

FIG. 15 shows an eighth embodiment of a BGA type semiconductor device 150 according to the present invention.

The semiconductor device 150 has such a structure that a heat releasing fin 151 is provided on the semiconductor device 140 of the seventh embodiment. The heat releasing fin 151 is adhered to the upper surface of the resin package 141 by the paste layer 152 having a high heat transfer rate.

FIG. 16 shows a ninth embodiment of a BGA type semiconductor device 160 according to the present invention.

The semiconductor device 160 has a structure such that a metal plate 161 is provided on the semiconductor device 140 of the seventh embodiment. The metal plate 161 is adhered to the upper surface of the resin package 141 by the paste layer 152 having a high heat transfer rate.

In the embodiments described above, stud bumps instead of the solder bumps 40 may be provided on the surface 32 a of the semiconductor chip 32. Also, pins may be used, replacing the solder balls 13A.

Furthermore, instead of the paste layer 43, a film having a high heat transfer rate may be used. Or the paste layer 43 may include Ag as a filler.

The additive layer 151 may have a two-layer structure.

Instead of the insulating paste having a high heat transfer rate used for the paste layer 44, an anisotropic conductive resin may be used. Also, the insulating paste may be used for forming the dam, replacing the dam member 33.

FIG. 17 shows a cross-sectional view of a tenth embodiment of a semiconductor device 200 according to the present invention. In brief, the semiconductor device 200 includes a semiconductor chip 201, a board 202, a sealing resin 203, external-connection balls 204, and a conductive member 205.

The semiconductor chip 201 is provided with internal-connection bumps 206 on a lower surface thereof, which are used as first electrodes to be connected to the board 202. The internal-connection bumps 206 are formed from solder, for example. The other (upper) surface of the semiconductor chip 201 is provided with an upper electrodes 206 which are used as a second electrode. In this embodiment, the upper electrode 207 is used as a ground electrode.

The board 202 is a multi-layered printed board which includes wiring layers 202 a inside an insulating layer 202 b made of glass-epoxy and the like. External-connection wirings 209 having a predetermined pattern are formed on an upper surface of the board 202. The external-connection wirings 209 include first external-connection wirings 209 a serving as signal lines and power lines, and second external-connection wirings 209 b serving as ground lines.

The semiconductor chip 201 is mounted on the board 202 by means of a flip-chip method. When the semiconductor chip 201 is mounted on the board 202, inner ends of the first external-connection wirings 209 a are connected to the internal-connection bumps 206 of the semiconductor chip 201. Also, inner ends of the second external-connection wirings 209 b are connected to the upper electrode 207 of the semiconductor chip 201 via the conductive member 205.

The external-connection wirings 209 and the wiring layers 202 a are lead to a back surface of the board 202 through vias 210 formed across layers inside the board 202. At the back surface of the board 202, the vias 210 are connected to the external-connection balls 204, which may be formed from solder, for example.

The external-connection balls 204 can be formed by arranging solder balls or arranging copper balls plated with solder. Or the external-connection balls 204 can be formed by applying heat-reflow treatment to solder paste which are arranged in predetermined locations by a screen-printing method.

The sealing resin 203 is formed to cover the conductive member 205 which is provided so as to cover the semiconductor chip 201. The sealing resin 203 serves to protect the semiconductor chip 201. Epoxy resin and the like may be used for the sealing resin 203.

The conductive member 205 is also a novel point of this embodiment, and is formed from silver paste, for example. The conductive member 205 is formed by potting the silver paste so as to cover the semiconductor chip 201.

The conductive member 205 is electrically connected to the upper electrode 207 formed on the upper surface of the semiconductor chip 201. Furthermore, the conductive member 205 is electrically connected to the second external-connection wirings 209 b at the upper surface of the board 202. Thus, the semiconductor chip 201 and the second external-connection wirings 209 b are electrically connected with each other via the conductive member 205.

FIG. 18 through FIG. 20 show structures of electrical connections between the semiconductor chip 201 and the external-connection wirings 209. In these figures, the sealing resin 203, the wiring layers 202 a, and the external-connection balls 204 are omitted for the sake of clarity.

FIG. 15 shows a structure of an electrical connection between the internal-connection bump 206 a formed on a signal pad of the semiconductor chip 201 and the first external-connection wirings 209 a.

As shown in FIG. 15, an insulating member 211 is provided between the semiconductor chip 201 and the board 202. Also, the insulating member 211 is formed on the first external-connection wirings 209 a at a connection point between the internal-connection bump 206 a formed on the signal pad and the first external-connection wirings 209 a.

Thus, the insulating member 211 electrically separates the first external-connection wirings 209 a from the conductive member 205. As a result, the upper electrode (ground electrode) 207 connected to the conductive member 205 is never short-circuited to the first external-connection wirings 209 a for conducting signals. Also, the insulating member 211 is formed from a resin which is a plastic, soft material. When heat is applied, stress is generated between the semiconductor chip 201 and the board 202 because of a difference in thermal-expansion coefficients of these two elements. However, the insulating member 211 can absorb the stress, thus enhancing the reliability of the semiconductor device 200.

FIG. 16 shows a structure of an electrical connection between the internal-connection bump 206 b formed on a ground pad of the semiconductor chip 201 and the second external-connection wirings 209 a.

As shown in FIG. 16, an insulating member 211 is not formed on the second external-connection wirings 209 b at a connection point between the internal-connection bump 206 b formed on the ground pad and the second external-connection wirings 209 b. Thus, the second external-connection wirings 209 b are exposed to the conductive member 205. As a result, the insulating member 205 is electrically connected with the second external-connection wirings 209 b and the internal-connection bump 206 b.

In summary, the insulating member 205 is electrically connected to the upper electrode 207 formed on the upper surface of the semiconductor chip 201, to the internal-connection bump 206 b formed beneath the lower surface of the semiconductor chip 201, and to the second external-connection wirings 209 b. Thus, the conductive member 205, the upper electrode 207, the internal-connection bump 206 b, and the second external-connection wirings 209 b are kept to the same ground level.

As shown in FIG. 17 and FIG. 19, the conductive member 205 has such a large volume that its inductance is lower than a wire connection. Thus, the electrical connection between the semiconductor chip 201 and the second external-connection wirings 209 b can have a suitable characteristic.

As shown in FIG. 19, the ground electrode is provided as the upper electrode 207 on the upper surface of the semiconductor chip 201. However, the ground electrode can also be provided beneath the lower surface of the semiconductor chip 201 as is the internal-connection bump 206 b.

Even when the ground electrodes are provided on both the upper and lower surfaces of the semiconductor chip 201, the same structure of the present invention as described above enables a connection between these ground electrodes and the second external-connection wirings 209 b via the conductive member 205. Thus, such a connection can be readily implemented in this embodiment of the present invention.

FIG. 20 shows a structure of an electrical connection between the upper electrode 207 formed on the semiconductor chip 201 and the second external-connection wirings 209 b at a location where no internal-connection bump 206 is provided.

As shown in FIG. 20, the conductive member 205 electrically connecting the upper electrode 207 and the second external-connection wirings 209 b is not limited to a location where the internal-connection bump 206 b is provided on the ground pad. That is, the conductive member 205 is also provided where no internal-connection bump 206 is formed. As in the above, the insulating member 211 is removed from the point of connection between the conductive member 205 and the second external-connection wirings 209 b.

As described above, in the semiconductor device 200 of the tenth embodiment of the present invention, the upper electrode 207 formed on the semiconductor chip 201 can be connected to the second external-connection wirings 209 b without relying on the internal-connection bump 206 for providing the connection. (The internal-connection bump 206 can be connected to the conductive member 205, but is not essential for establishing the electrical connection between the upper electrode 207 and the second external-connection wirings 209 b.) Thus, the number of the internal-connection bumps 206 provided beneath the lower surface of the semiconductor chip 201 can be reduced. This leads to an extra space being provided for the arrangement of the internal-connection bumps 206.

Also, the second external-connection wirings 209 b can be formed at any location on the board 202 as long as the conductive member 205 is provided at that location. This means that there is a wider scope for the arrangement of the second external-connection wirings 209 b. For example, the second external-connection wirings 209 b can be formed at locations where the first external-connection wirings 209 a are not provided. Thus, the second external-connection wirings 209 b can be arranged without a strenuous effort.

As described above, in the semiconductor device 200 of the tenth embodiment of the present invention, there is a wider scope for the arrangement of the internal-connection bumps 206 and the external-connection wirings 209. Thus, the manufacturing of the semiconductor device 200 can be easier, which leads to an improved yield.

Also, the conductive member 205 which is connected to the ground electrode and covers the semiconductor chip 201 can serve as a shielding member for the semiconductor chip 201. Thus, the shielding of the semiconductor chip 201 can be ensured, which leads to prevention of the malfunctions of the semiconductor chip 201.

The tenth embodiment has been described particularly with regard to a configuration in which the conductive member 205 serving as a ground wiring is connected with the upper electrode 207 serving as the ground electrode and with the internal-connection bump 206 b. However, another configuration may be employed in which the conductive member 205 is connected to the power electrodes or the signal electrodes.

FIG. 21 shows a cross-sectional view of an eleventh embodiment of a semiconductor device 220 according to the present invention. In FIG. 21, the same element as those of FIG. 17 are referred by the same numerals.

In the eleventh embodiment, the board 202 is a multi-layered printed wiring board in which the wiring layers 202 a and the vias 210 are formed inside the insulating layer 202 b made of glass-epoxy. The eleventh embodiment is characterized in that a multi-layered ceramic wiring board 221 and a metal board 222 are used as boards.

In brief, the semiconductor device 220 includes the semiconductor chip 201, the multi-layered ceramic wiring board 221, the metal board 222, a cap 223, the external-connection balls 204, and the conductive member 205.

The multi-layered ceramic wiring board 221 includes wiring layers 221 a and vias 221 b connecting between the wiring layers 221 a. Furthermore, the external-connection balls 204 are provided beneath the lower surface of the multi-layered ceramic wiring board 221, and are electrically connected to the relevant wiring layers 221 a via the vias 221 b.

A cavity 225 is formed at a general center of the multi-layered ceramic wiring board 221, and houses the semiconductor chip 201. An opening of the cavity 225 is provided with the cap 223 made of metal, which is fixed by means of a connection member 226. The cap 223 seals the cavity 225.

Beneath the lower surface of the metal board 222 is formed an insulating layer 224. The external-connection wirings 209 are provided beneath the lower surface of the insulating layer 224. The internal-connection bumps 206 are connected to the external-connection wirings 209 so that the semiconductor chip 201 is connected to the metal board 222 by means of a flip-chip method. The multi-layered ceramic wiring board 221 is fixed with an adhesive and the like on one side of the metal board 222 where the semiconductor chip 201 is provided.

The upper electrode 207 is formed on the surface of the semiconductor chip 201 opposite the surface on which the internal-connection bumps 206 are formed. In this embodiment, the upper electrode 207 is electrically connected to the external-connection wirings 209 via the conductive member 205 as in the previous embodiment.

In the semiconductor device 220 having what is called a ceramic-package structure using the multi-layered ceramic wiring board 221, the conductive member 205 can be used for electrically connecting the upper electrode 207 and the external-connection wirings 209. Accordingly, there is a wider scope for the arrangement of the internal-connection bumps 206 and the external-connection wirings 209. Thus, the manufacturing of the semiconductor device 220 can become easier, which leads to an improved yield at a time of implementation.

FIG. 22 shows a cross-sectional view of an twelfth embodiment of a semiconductor device 230 according to the present invention. In FIG. 22, the same element as those of FIG. 17 are referred by the same numerals.

In this embodiment, a plurality (four in the figure) of semiconductor chips 201A through 201D are packaged and provided on a wiring board 231. The twelfth embodiment is characterized in that the semiconductor device 230 is made into a multi-chip module (MCM).

In brief, the semiconductor device 230 includes the semiconductor chips 201A through 201D, the wiring board 231, a ceramic board 232, leads 233, a cap 236, and the conductive member 205.

The wiring board 231 is provided at an upper surface thereof with external-connection wirings (not shown), and the semiconductor chips 201A through 201D are connected to the wiring board 231 by means of a flip-chip method. The insulating member 211 is provided between each of the semiconductor chips 201A through 201D and the wiring board 231. Thus, as is described with reference to FIG. 18 through FIG. 20, some of the internal-connection bumps 206A through 206D are appropriately insulated from the conductive member 205.

The wiring board 231 is mounted on the ceramic board 232, whose perimeter is provided with a ceramic frame 234 having a frame shape. The leads 233 are fixed between the ceramic board 232 and the ceramic frame 234. An inner lead portion 233a of the leads 233 is electrically connected to the external-connection wirings formed on the wiring board 231 via wires 235. The cap 236 is provided at an upper opening of the ceramic frame 234, sealing the semiconductor chips 201A through 201D.

Upper electrodes 207A through 207D are, respectively, formed on the surfaces of the semiconductor chips 201A through 201D opposite the surfaces on which the internal-connection bumps 206A through 206D are formed. In this embodiment, the upper electrodes 207A through 207D are electrically connected to the external-connection wirings via the conductive member 205 as in the previous embodiments. Thus, the upper electrodes 207A through 207D formed on the semiconductor chip 201A through 201D, respectively, are kept to the same voltage level (e.g., the ground level).

As described above, in the semiconductor device 230 having the MCM package structure, the upper electrodes 207A through 207D can be connected to the external-connection wirings via the conductive member 205. Thus, the manufacturing of the semiconductor device 230 can be made easier, and the yield at a time of the implementation can be improved.

FIG. 23 shows a cross-sectional view of a thirteenth embodiment of a semiconductor device 240 according to the present invention. In FIG. 23, the same elements as those of FIG. 17 are referred by the same numerals.

This embodiment is characterized in that the semiconductor device 240 has a chip-on-chip structure by piling two semiconductor chips 201 and 241 one over the other.

In brief, the semiconductor device 240 includes the semiconductor chips 201 and 241, the board 202, an insulating member 242, the sealing resin 203, the external-connection balls 204, and the conductive member 205.

The semiconductor chip 241 is electrically connected to the external-connection wirings 209 formed on the board 202 via wires 243. Electrodes (not shown) are provided on an upper surface of the semiconductor chip 241, and are electrically connected to the semiconductor chip 201. These electrodes are connected to the internal-connection bumps 206 formed on the semiconductor chip 201, so that the semiconductor chip 201 is connected to the upper surface of the semiconductor chip 241 by means of a flip-chip method. Thus, the semiconductor chip 201 ends up being mounted on the semiconductor chip 241.

The insulating layer 242 is provided to cover the semiconductor chip 241 and to cover part of the semiconductor chip 201. Thus, the points of electrical connection between the semiconductor chips 201 and 241 are insulated from the conductive member 205. Furthermore, the sealing resin 203 is provided to cover an upper surface of the conductive member 205.

The upper electrode 207 is provided on the surface of the semiconductor chip 201 opposite the surface on which the internal-connection bumps 206 are formed. The upper electrode 207 is electrically connected to the external-connection wirings 209 b formed on the board 202 via the conductive member 205.

As described above, in the semiconductor device 240 having the chip-on-chip structure, the upper electrode 207 can be connected to the external-connection wirings 209 b via the conductive member 205. Thus, the manufacturing of the semiconductor device 240 can be made easier, and the yield at a time of the implementation can be improved.

As described above, the semiconductor device according to the present invention can provide a wiring pattern on the additive layer without a restriction posed by the through-holes. Thus, for example, a wiring pattern traversing through-holes can be laid on the additive layer. In this manner, the path length of wiring patterns in the semiconductor devices having nodes beneath an assembly board can be reduced when compared with the case of the related art. As a result, compared to the related art, a better signal propagation characteristic can be obtained for signals having a high frequency.

Furthermore, the semiconductor device according to the present invention can lower an inside heat resistance, compared to semiconductor devices of the related art. Thus, the semiconductor device of the present invention can enhance a heat releasing characteristic, yet can properly seal the semiconductor chip inside.

Also, the semiconductor device according to the present invention can reduce the density of electrode arrangement, compared to a configuration in which all the electrodes are provided on the same surface of the semiconductor chip. Thus, the external-connection nodes can be arranged with a high density so as to be easily manufactured, leading to an improved yield.

Furthermore, the semiconductor device according to the present invention has the conductive member covering the semiconductor chip, so that the low inductance of the conductive member can provide better electrical characteristics. Also, when the conductive member is coupled to the ground level, the conductive member can serve as a shield for the semiconductor chip.

Furthermore, the semiconductor device according to the present invention can electrically connect the external-connection wirings with appropriate electrodes of the semiconductor chip via the conductive member. Thus, there is a wider scope for the arrangement of the external-connection wirings.

Also, the semiconductor chip according to the present invention provides the insulating member which can properly insulate the internal-connection bumps from each other or from the conductive member.

Furthermore, the present invention can be applied to the multi-chip module structure.

Furthermore, the present invention can be applied to the chip-on-chip structure.

In the following, another aspect of the present invention will be described.

Semiconductor devices have been experiencing an increase in circuit density, and a demand for a higher assembly density is also on increase.

Semiconductor devices of a BGA (ball-grid array) type can achieve a narrower pitch of external connection nodes (i.e., bumps, lands, etc) than can semiconductor devices of a QFC (quad flat package) type. Because of this, BGA-type semiconductor devices attracted attention, and have been reduced to practice.

In addition to the trend described above, there has been a tendency that heat released from semiconductor devices is increased as a greater circuit density is achieved. This necessitates measures to be taken to enhance heat releasing characteristics of semiconductor devices.

Examples of a semiconductor device which has a narrower pitch of external connection nodes and improved heat releasing characteristics include a device disclosed in Japanese Patent Laid-open Application No.8-17964.

The semiconductor device of this publication includes a board, a semiconductor device, a dam member (frame-shape member), and a metal plate (plate-shape member) among other elements. The board is a printed board (resin board), and the semiconductor device is connected on the print board through face-down bonding. In detail, the semiconductor device is provided with electrodes on a bottom surface thereof, and bumps are formed on these electrodes. The bumps are connected to respective electrode portions on the board, thereby connecting the semiconductor device to the board.

The dam member has a frame shape having a rectangular hole at a center thereof, and is made of the same material as that of the board. The dam member is fixed on the board with adhesive. With the dam member being provided on the board, the semiconductor device is situated inside the hole of the dam member.

The metal plate is provided to cover the semiconductor device and the dam member mounted on the board, and is glued on the semiconductor device and the frame-shape member by using adhesive. On the bottom surface of the board are provided bumps, which are to be connected to another board for assembly.

The semiconductor device described above can achieve a bump arrangement at a narrow pitch because of a BGA-type structure thereof. Further, the metal plate serves as a means for releasing heat, so that heat generated by the semiconductor device can be efficiently released.

Materials used for the dam member and the metal plate, however, are different from each other. Because of this, when an environmental test (temperature-cycle test) is conducted, an excessive force may be applied to the connection point between the semiconductor device and the board due to differences in material characteristics (e.g., a thermal-expansion coefficient).

The dam member and the board are made of the same material which is used for the print board (resin board), whereas the metal plate is formed from aluminum or the like for the purpose of heat releasing. A thermal-expansion coefficient is different between resin and metal. When a glass-epoxy board is used as a resin board, a thermal-expansion coefficient of the metal plate is greater than that of the dam member and the board.

As mentioned above, semiconductor devices are subjected to a set of reliability tests before shipping from the factory. One of the reliability tests is a burn-in test. The burn-in test exposes a semiconductor device to a heating process and a cooling process in turn at a predetermined cycle, and a check is made as to whether any abnormality is developed.

Where the thermal-expansion coefficient of the dam member and the board differs significantly from the thermal-expansion coefficient of the metal plate, a degree of expansion and contraction is quite different between the metal plate and a portion of dam member and the board when the burn-in test is conducted.

Since the semiconductor device has a bottom surface thereof attached to the board and a top surface thereof is connected to the metal plate. Because of this configuration, the semiconductor device may break off from the board, or a crack may develop at the bump-connection portion between the semiconductor device and the board. This undermines reliability of the semiconductor device.

Accordingly, there is a need for a semiconductor device which can maintain reliability even when a heating process is applied as in the temperature-cycle test.

FIGS. 24 and 25 are illustrative drawing for explaining a fourteenth embodiment through a sixteenth embodiment of the present invention.

The embodiments described in the following are characterized by material characteristics of each element which makes up a semiconductor device 310, so that drawings showing each embodiment are the same. In the following, therefore, the fourteenth embodiment will be described first with reference to FIG. 24 and FIG. 25, and the fifteenth and sixteenth embodiments will be described by focusing on differences from the fourteenth embodiment.

In what follows, the fourteenth embodiment of the present invention will be described with reference to FIG. 24 and FIG. 25. The semiconductor device 310 of the fourteenth embodiment includes a print board 312, a semiconductor device 314, a stiffener (frame-shape member) 316, and a metal plate (plate-shape member) 318.

The print board 312 is made of a family of glass epoxy, and has a multi-layer structure in which wires are laid out. The print board 312 has an upper surface thereof, on which device electrodes (not shown) are provided to establish connection with the semiconductor device 314. A lower surface of the print board 312 is provided with external-connection electrodes (not shown), which are connected to solder balls 322 serving as external-connection nodes. A thermal-expansion coefficient α₃ of the print board 312 is 13×10⁻⁶ to 15×10⁻⁶ (1/° C.), for example.

The semiconductor device 314 is provided in a bare-chip condition, and has a lower surface thereof provided with a number of connection bumps 320. This lower surface opposes the print board 312. The semiconductor device 314 is connected to the upper surface of the print board 312 by face-down bonding. In detail, the connection bumps 320 formed on the lower surface of the semiconductor device 314 are connected to the device electrodes provided on the upper surface of the print board 312. This achieves electrical connection between the semiconductor device 314 and the print board 312.

After connecting the semiconductor device 314 to the print board 312, a gap between the semiconductor device 314 and the print board 312 is filled with an under-fill resin 332. The under-fill resin 332 serves to step up strength of connection between the connection bumps 320 and the print board 312, thereby enhancing reliability.

As previously described, the print board 312 has a multi-layer structure containing internal wires. These internal wires electrically connect the device electrodes formed on the upper surface to the external-connection electrodes provided on the lower surface. Further, the external-connection electrodes is provided with the solder balls 322, so that the semiconductor device 314 is electrically connected to the solder balls 322 via the device electrodes, the internal wires, and the external-connection electrodes.

The stiffener 316 has an opening 330 formed at a center thereof and having a rectangular shape, so that the stiffener 316 has a frame shape. The stiffener 316 is made of alumina, a thermal-expansion rate α₁ of which is approximately 7.0×10⁻⁶ (1/° C.). As can be seen when looking at the shape of the corner recess 334, each corner of the opening 330 is provided with a corner recess 334, which has a partially circular shape when viewed from the top.

The stiffener 316 is glued to the upper surface of the print board 312 by using a first adhesive 324. With the stiffener 316 being provided on the print board 312, the semiconductor device 314 is situated approximately at the center of the opening 330.

The metal plate 318 is a plate-shape member made of metal, and, for example, formed from aluminum which has a sufficient heat conductivity. The metal plate 318 functions as a heat releasing plate, and covers the semiconductor device 314 and the stiffener 316 provided on the print board 312.

The semiconductor device 314 and the metal plate 318 are connected together via a device adhesive 328. Further, the stiffener 316 and the metal plate 318 are connected together via a second adhesive 326. In this manner, the metal plate 318 is fixedly connected to the semiconductor device 314 and the stiffener 316. The metal plate 318 has a thermal-expansion coefficient α₂ thereof which is approximately 23×10⁻⁶ (1/° C).

The semiconductor device 310 having the configuration as described above is classified as one of the BGA-type semiconductor devices, and has a narrower pitch of the solder balls 322 in comparison with a QFP-type semiconductor device. As described above, the metal plate 318 serves as a heat releasing plate, heat generated by the semiconductor device 314 can be effectively released.

The semiconductor device 310 described above is subjected to a predetermined set of reliability tests before shipment from the factory. On the of reliability tests is a burn-in test which exposes the semiconductor device to a heating process. In the burn-in test, the semiconductor device 310 is subjected to a heating process (e.g., heated to 125° C.) and a cooling process (e.g., cooled to −55° C.) in turn.

As described above, the thermal-expansion coefficient of the print board 312 is different from the thermal-expansion coefficient of the metal plate 318. Because of this, where the stiffener 316 and the print board 312 have similar thermal-expansion coefficients, a stress is developed during the burn-in test between the connection bumps 320 and the print board 312 due to the difference in the thermal-expansion coefficients. This may result in the connection bumps 320 breaking off from the print board 312. The similar situation may be observed where the stiffener 316 and the metal plate 318 have thermal-expansion coefficients close to each other.

To counter this problem, this embodiment employs the stiffener 316 which has a sufficient sturdiness, so that the stiffener 316 can prevent the print board 312 and the metal plate 318 from deforming from heat-induced expansion.

In detail, the thermal-expansion coefficient α₁ of the stiffener 316, the thermal-expansion coefficient α₂ of the metal plate 318, and a thermal-expansion coefficient α₃ of the print board 312 are selected to relate as:

α₁≦(α₂+α₃)/2  (1)

Namely, the thermal-expansion coefficient α₁ of the stiffener 316 is selected to be smaller than an average of the thermal-expansion coefficient α₂ of the metal plate 318 and the thermal-expansion coefficient α₃ of the print board 312.

Where the thermal-expansion coefficient α₂ of the metal plate 318 is greater than the thermal-expansion coefficient α₃ of the print board 312, and, therefore, a difference in thermal expansion is observed between the print board 312 and the metal plate 318, the stiffener 316 serves through the sturdiness thereof to lessen the heat-induced expansion of the metal plate 318, thereby preventing a strong stress from being applied to the connection points between the print board 312 and the semiconductor device 314. This successfully avoids cracking or disconnecting at the connection points between the semiconductor device 314 and the print board 312.

In this manner, a temperature-cycle test such as the burn-in test can be conducted on the semiconductor device 310 without inflicting damage to the semiconductor device 310. This improves a yield rate and the reliability of the semiconductor device 310.

Despite a need to satisfy the equation (1), control of the individual thermal-expansion coefficients is practically impossible. Alternately, appropriate materials are selected for the print board 312, the stiffener 316, and the metal plate 318 such that the conditions set forth in the equation (1) are met.

Appropriate combinations of the materials for the print board 312, the stiffener 316, and the metal plate 318 may include the following ones.

1) BT resin for the print board 312, alumina for the stiffener 316, and aluminum for the metal plate 318 (i.e., the combination of the above-described embodiment)

2) BT resin for the print board 312, alumina for the stiffener 316, and copper for the metal plate 318

3) BT resin for the print board 312, aluminum for the stiffener 316, and copper for the metal plate 318

4) BT resin for the print board 312, aluminum nitride for the stiffener 316, and aluminum for the metal plate 318

FIG. 26 is a table chart showing results of experiments which were conducted to check the number of defective devices after performing a temperature-cycle test on the semiconductor device 310. The results are shown with respect to the four different combinations described above.

In this experiment, one cycle is comprised of a cooling process to expose devices to −55° C. temperature and a heating process to expose the devices to 125° C. temperature, and this cycle is repeated 50 times (shown as 50C in the table chart), 100 times (shown as 100C), 200 times (shown as 200C), or 300 times (shown as 300C). A ratio of the number T of defective devices to the total number C of all the devices subjected to the test is shown. For a comparison purpose, two related-art combinations of materials were also subjected to the test. These combinations include:

5) BT resin for the print board 312, BT resin for the stiffener 316, and copper for the metal plate 318; and

6) BT resin for the print board 312, Cobal for the stiffener 316, and copper-tungsten alloy for the metal plate 318.

As shown in the table chart, the combination 5) resulted in all the devices suffering some defects after 100 cycles. Further, all the devices of the combination 6) sustained defects after 200 cycles.

In comparison, the combinations 1) through 4) of the present invention suffered no defect even after 300 cycles. In this manner, the configuration according to the present invention can protect the semiconductor device 310 from any damages caused by the temperature-cycle test such as a burn-in test. The results of the experiments clearly show that the yield rate and the reliability of the semiconductor device 310 can be enhanced.

As previously described, the semiconductor device 310 according to the present invention is provided with the corner recess 334 at each corner of the opening 330. This corner recess 334 prevents cracks from developing at the corners of the opening 330 formed through the stiffener 316.

Namely, when a heat process is applied as part of a temperature test or the like, the stiffener 316 experiences heat-induced expansion and contraction in turn. If the corners of the opening 330 are formed to have a right angle, a stress generated by the expansion and the contraction may concentrate on the corner, thereby developing cracks. The present invention provides the corner recess 334 at each corner of the opening 330, however, so that the stress created by the expansion and the contraction is evenly distributed over the corner recess 334, thereby preventing cracks form being formed. In this manner, the corner recess 334 provided at the corners of the opening 330 can also contribute to an enhancement in the yield rate and the reliability of the semiconductor device 310.

In what follows, the fifteenth embodiment of the present invention will be described.

It should be noted that the fifteenth embodiment described is characterized by material characteristics of each element which makes up the semiconductor device 310, so that drawings showing this embodiment are the same as those used in the previous embodiment. In the following, therefore, the fifteenth embodiment will be described with reference to FIG. 24 and FIG. 25 by specifically referring to differences from the fourteenth embodiment.

In the fourteenth embodiment, the sturdiness of the stiffener 316 was relied upon in order to prevent the print board 312 and the metal plate 318 from deforming at the time of the heating process, and the reliability of the semiconductor device 310 against the temperature-cycle test was insured by such a configuration.

In the fifteenth embodiment, on the other hand, the first adhesive 324 between the print board 312 and the stiffener 316 and the second adhesive 326 between the metal plate 318 and the stiffener 316, or at least one of these adhesives, are relied upon in order to absorb heat-induced deformation of the print board 312 and the metal plate 318. Here, the device adhesive 328 should also be selected to have the same effect as described above.

A description in the following will be given by taking as an example a case in which the metal plate 318 and the stiffener 316 are made of the same material (e.g., metal such as aluminum), and in which the print board 312 is formed from resin (e.g., BT resin).

In this configuration, the stiffener 316 and the metal plate 318 have a greater thermal-expansion coefficient than the print board 312. Because of this, is quite possible that a strong stress is developed between the semiconductor device 314 and the print board 312 when a burn-in test is conducted as a temperature-cycle test.

To counter this problem, this embodiment uses the first adhesive 324 that retains elasticity to a certain degree even after coagulation thereof when the first adhesive 324 fixedly connects the stiffener 316 with the print board 312. In this configuration, the first adhesive 324 is sufficiently elastic to deform, thereby absorbing a relative displacement between the print board 312 and the stiffener 316 (and the metal plate 318) created by the heat-induced expansion.

In this manner, the stress applied to the connection points between the semiconductor device 314 and the print board 312 can be reduced, so that cracks and/or breaking off are not developed at those connection points. Reliability of the semiconductor device 310 is thus retained.

In this configuration, the device adhesive 328 should have the same elastic nature as described above since the device adhesive 328 connects the semiconductor device 314 with the metal plate 318.

Where the print board 312 and the stiffener 316 are made of the same material, and the metal plate 318 has different material characteristics, the second adhesive 326 should be chosen so as to have a sufficient elasticity.

In what follows, the sixteenth embodiment of the present invention will be described.

The sixteenth embodiment uses the print board 312 and the metal plate 318 that have substantially the same sturdiness (thermal sturdiness). This configuration prevents a deformation from developing between the print board 312 and the metal plate 318 due to a thermal-expansion difference even when a heat process is applied to the semiconductor device 310 as part of the temperature-cycle test. Because of this, no breaking off or cracking is brought about at the connection points between the semiconductor device 314 and the print board 312, thereby maintaining reliability of the semiconductor device 310.

In what follows, a detailed description will be given with regard to how to achieve a substantially equal sturdiness (thermal sturdiness) between the print board 312 and the metal plate 318.

A Young coefficient E_(P) and a Poisson ratio V_(P) of the print board 312 are used for representing the sturdiness G_(P) as follows.

G_(P)=E_(P)/)2(1+V_(P))  (2)

Likewise, a sturdiness GM of the metal plate 318 is represented by a Young coefficient E_(M) and a Poisson ratio V_(M) of the metal plate 318 as follows.

G_(M)=E_(M)/(2(1+V_(M))  (3)

Further, a thermal-expansion coefficient α_(P) and a volume V_(P) of the print board 312, a thermal-expansion coefficient α_(M) and a volume V_(M) of the metal plate 318, a thermally induced extension L_(P) of the print board 312 heated to a predetermined temperature, and a thermally induced extension L_(M) of the metal plate 318 heated to this temperature are related as:

L_(P)=G_(P)×α_(P)×V_(P)  (4)

L_(M)=G_(M)×α_(M)×V_(M)  (5)

In order to equalize a thermal sturdiness between the print board 312 and the metal plate 318, L_(P) and L_(M) should be equal to each other. Therefore,

G_(P)×α_(P)×V_(P)≈G_(M)×α_(M)×V_(M)  (6)

should be satisfied by the involved parameters.

The sturdiness G_(P) and G_(M) and the thermal-expansion coefficients α_(P) and α_(M), however, are inherent to each material, and are fixed when materials for the print board 312 and the metal plate 318 are selected. Practically variable parameters among those which appear in the equation (6) are the volumes V_(P) and V_(M), which are thus adjusted to satisfy the equation (6) in practice.

When the volumes V_(P) and V_(M) are adjusted to meet the conditions set forth in the equation (6), no relative displacement is generated by thermal expansion between the print board 312 and the metal plate 318 even when the temperature-cycle test is conducted. This can reduce a stress applied to the connection points between the semiconductor device 314 and the print board 312. In this manner, this embodiment can prevent breaking off or cracking at the connection points between the semiconductor device 314 and the print board 312, thereby maintaining reliability of the semiconductor device 310.

According to the present invention, the frame-shape member is connected to the upper surface of the board with first adhesive, and, also, the semiconductor chip is mounted on the upper surface of the board. The plate-shape member is further connected to the semiconductor chip and the frame-shape member with second adhesive so as to cover the semiconductor chip and the frame-shape member. This configuration has the board with the semiconductor chip mounted thereon, the frame-shape member, and the plate-shape member stacked one over another in this order from the bottom to the top.

Since the frame-shape member has a sufficient sturdiness that can prevent thermal-expansion-induced deformations of the board and the plate-shape member, the board and the plate-shape member do not suffer significant deformation even when the semiconductor device is subjected to a test involving heating of the device (e.g., a burn-in test).

Accordingly, a heat process such as that applied as part of a temperature-cycle test creates less heat-induced displacement between the board and the plate-shape member than it otherwise would do, so that a stress applied to the connecting points between the semiconductor chip and the board can be reduced. This prevents breaking off or cracking at the connection points between the semiconductor chip and the board, thereby maintaining reliability of the semiconductor device.

According to another aspect of the present invention, a thermal-expansion coefficient α₁ of the frame-shape member, a thermal-expansion coefficient α₂ of the plate-shape member, and a thermal-expansion coefficient of α₃ of the board are related as α₁≦(α₂α₃)/2. That is, the thermal-expansion coefficient α₁ of the frame-shape member is smaller than an average of the thermal-expansion coefficient α₂ of the plate-shape member and the thermal-expansion coefficient of α₃ of the board.

Accordingly, when the thermal-expansion coefficient of the plate-shape member is far greater than that of the board, for example, the frame-shape member serves to mitigate the heat-induced deformation of the plate-shape member, thereby partially preventing the deformation of the plate-shape member from propagating to the board and to the semiconductor chip.

According to another aspect of the present invention, materials of the frame-shape member and the plate-shaped member are preferably alumina and aluminum, respectively.

According to another aspect of the present invention, materials of the frame-shape member and the plate-shaped member are preferably alumina and copper, respectively.

According to another aspect of the present invention, materials of the frame-shape member and the plate-shaped member are preferably aluminum nitride and copper, respectively.

According to another aspect of the present invention, materials of the frame-shape member and the plate-shaped member are preferably aluminum nitride and aluminum, respectively.

According to another aspect of the present invention, a round-shape recess is provided at each corner of the opening of the frame-shape member, thereby preventing a crack from developing at a respective corner. This measure is taken in consideration of the following. If the corners of the opening are formed to have a right angle, a stress generated by the heat-induced expansion and the contraction may concentrate on the corners when a heat process is applied as in a temperature-cycle test, thereby developing cracks.

According to another aspect of the present invention, at lest one of the first adhesive and the second adhesive has a sufficient elasticity to absorb heat-induced deformations of the board and the plate-shape member. Even when a heat process is applied as in a temperature-cycle test, therefore, a heat-induced relative displacement between the board and the plate-shape member is absorbed by the at least one of the first adhesive and the second adhesive owing to the sufficient elasticity thereof. This reduces a stress applied to the connecting points between the semiconductor chip and the board. This prevents breaking off or cracking at the connection points between the semiconductor chip and the board, thereby maintaining reliability of the semiconductor device.

According to another aspect of the present invention, a package assembly includes a board and a frame-shape member which is connected to an upper surface of the board with adhesive, and has an opening to accommodate a semiconductor chip therein, wherein the frame-shape member has such a sufficient sturdiness that prevents thermal-expansion-induced deformation of the board.

In this package assembly, the frame-shape member has a sufficient sturdiness that can prevent thermal-expansion-induced deformation of the board, so that the board does not suffer significant deformation even when the semiconductor device is subjected to a test involving heating of the device (e.g., a burn-in test).

Further, the present invention is not limited to these embodiments, but various variations and modifications may be made without departing from the scope of the present invention. 

What is claimed is:
 1. A semiconductor device comprising: a board; a semiconductor chip which is connected to an upper surface of the board by use of bumps; a frame-shape member which is connected to said upper surface of said board with first adhesive, and has an opening to accommodate said semiconductor chip therein and a recess provided at each comer of said opening; and a plate-shape member which is situated to cover said semiconductor chip and said frame-shape member, and is connected to said semiconductor chip and said frame-shape member with second adhesive, wherein a modulus of rigidity G_(P), a thermal expansion coefficient α_(P), and a volume V_(P) of said board are related with a modulus of rigidity G_(M), a thermal expansion coefficient α_(M), and a volume V_(M) of said plate-shape member such that G_(P)×α_(P)×V_(P) is substantially equal to G_(M)×α_(M)×V_(M), and said frame-shape member has a sufficient sturdiness to substantially prevent deformations of said board and said plate-shape member.
 2. The semiconductor device as claimed in claim 1, wherein a thermal-expansion coefficient α₁ of said frame-shape member, a thermal-expansion coefficient α₂ of said plate-shape member, and a thermal-expansion coefficient of α₃ of said board are related as: α₁≦(α₂+₃)/2.
 3. The semiconductor device as claimed in claim 1, wherein said frame-shape member comprises alumina and said plate-shape member comprises aluminum.
 4. The semiconductor device as claimed in claim 1, wherein said frame-shape member comprises alumina and said plate-shape member comprises copper.
 5. The semiconductor device as claimed in claim 1, wherein said frame-shape member comprises aluminum nitride and said plate-shape member comprises copper.
 6. The semiconductor device as claimed in claim 1, wherein said frame-shape member comprises aluminum nitride and said plate-shape member comprises aluminum.
 7. The semiconductor device as claimed in claim 1, wherein said frame-shape member has a corner recess of a round shape provided at each corner of said opening.
 8. A package assembly comprising: a board having an upper surface; a frame-shape member which is connected to said upper surface of said board with adhesive, and has an opening to accommodate a semiconductor chip therein and a recess provided at each comer of said opening, and a plate-shape member situated to cover said frame-shape member and said opening and connected to said frame-shape member with adhesive, wherein a modulus of rigidity G_(P), a thermal expansion coefficient α_(P), and a volume V_(P) of said board are related with a modulus of rigidity G_(M), a thermal expansion coefficient α_(M), and a volume V_(M) of said plate-shape member such that G_(P)×α_(P)×V_(P) is substantially equal to G_(M)×α_(M)×V_(M), and said frame-shape member has a sufficient sturdiness to substantially prevent deformation of said board.
 9. The package assembly as claimed in claim 8, wherein a thermal-expansion coefficient α₁ of said frame-shape member, a thermal-expansion coefficient α₂ of said plate-shape member, and a thermal-expansion coefficient of α₃ of said board are related as: α₁≦(α₂+α₃)/2.
 10. The package assembly as claimed in claim 8, wherein said frame-shape member comprises alumina and said plate-shape member comprises aluminum.
 11. The package assembly as claimed in claim 8, wherein said frame-shape member comprises aluminum and said plate-shape member comprises copper.
 12. The package assembly as claimed in claim 8, wherein said frame-shape member comprises aluminum nitride and said plate-shape member comprises copper.
 13. The package assembly as claimed in claim 8, wherein said frame-shape member comprises aluminum nitride and said plate-shape member comprises aluminum.
 14. The package assembly as claimed in claim 8, wherein said frame-shape member has a corner recess of a round shape provided at each corner of said opening. 